1. Field of the Invention
The present invention relates to a device for the posterior dynamic guidance of the spine, which is intended to be implanted along the posterior side of the spinal column in order to guide the movements of two adjacent vertebrae one relative to the other, by reproducing an intervertebral articulated joint. The invention also relates to a unit comprising at least two of these devices, and to a spinal treatment system comprising such a device.
The invention thus relates to the treatment of degenerative spine disease or spinal trauma, particularly in the dorso-lumbar region of the spinal column, but also in the region of the cervical spine.
2. Brief Description of the Related Art
To treat intervertebral instability one known first option is to fuse two adjacent vertebrae, which amounts to depriving these two vertebrae of any freedom of relative movement. Completely rigid fixators are therefore implanted fixedly along the spine to permanently immobilize the joint between the two vertebrae that are to be fused. This arthrodesis intervention does, however, lead to degeneration of the adjacent disks which then often require later treatment.
Another known treatment option is to operate at an earlier stage than an arthrodesis would require and is aimed at implanting a posterior dynamic guidance device as proposed for example in WO-A-03/094699. For this purpose, the device comprises, first, bone anchoring screws for anchoring into the posterior side of two adjacent vertebrae and, second, elastic elements connecting these screws. These elastic elements are, in theory, intended to relieve the load on the intervertebral disk and correct any excessive pressure on the articulation surfaces between this disk and the vertebrae. By comparison with an arthrodesis treatment, this type of device offers the patient greater comfort because it allows the mobility of the spine to be maintained. However, in practice, it proves tricky to use: it is difficult to determine the elasticity of the connecting elements because this elasticity has to be tailored to each patient according to his surgical requirement and build. In addition, ultimately there is a risk that the elastic behavior of these elastic elements may change. Imperfect control of the parameters relating to the elasticity of these elements means that the desired spinal mobility cannot be guaranteed and this may lead to mediocre guidance or even to instability in the intervertebral gap and aggravate the lesions that the intervention was supposed to be treating.